15.4.4.2 The Print Command With Objective-C

The print command has also been extended to accept methods. For example:

print -[object hash]

will tell gdb to send the hash message to object
and print the result. Also, an additional command has been added,
print-object or po for short, which is meant to print
the description of an object. However, this command may only work
with certain Objective-C libraries that have a particular hook
function, _NSPrintForDebugger, defined.